Discussion

Agar is a complex mixture of polysaccharides extracted from species of the red algae known as the agarophytes (Duckworth, Hong, & Yaphe, 1970). Agar is composed of alternating β(1,3)- and α(1,4)-linked galactose residues and is lightly sulfated. Early investigation by Araki (1937) on the agar from Gelidium amansii showed that agar consists of two major fractions: agarose, a neutral polymer, and agaropectin, a sulphated polymer. However, later work has shown that agar is actually composed of a complex mixture of polysaccharides instead of one neutral and one anionic polysaccharide. Stanley (2006) stated that the complex mixture of polysaccharides range from a virtually uncharged molecule (the unsubstituted polymer of agarobiose, which is shown in Figure (1.1) to various charged galactans, some rich in ester sulfate, others in pyruvate, which occur as the ketal across positions 4- and 6- in the (1,3)-linked galactose residues [4,6-Ο- (I’-carboxyethylidene)- D-galactose]. Agarose gels, which consist of thick bundles of agarose chains and large pores of water, exhibit strong elasticity and high turbidity (Aymard et al., 2001). (Braudo et al. 1991) considered hydrogen bonding to be the primary mechanism involved in agarose gelation. Agarose in solution exists as random coils and when the solution is cooled the coils become ordered, thus, the agarose gels are formed. As cooling progresses, doubles helices are formed for gel network (Arnott et al., 1974). Arnott et al. (1974) further suggested that the helices are aggregated due to the turbidity of gels and the behavior of short, helix-forming chains in precipitating from solution as soon as they begin to undergo the transition to double helices (Dea, McKinnon, & Rees, 1972).